Servo valve

ABSTRACT

The present invention relates to an improved electricallyoperated hydraulic servo valve in which a force feedback system is employed in positioning a spool and more particularly to improvements in the connection between the spool and a feedback spring, in which one end of the feedback spring is integrally connected with the spool and at the same time the feedback spring is made to have a flexibility in a direction perpendicular to that of movement of the spool as well in order to accommodate the difference in locus between a circular motion of the feedback spring and a linear motion of the spool.

Takahashi et al.

[ June 4, 1974 SERVO VALVE [75] Inventors: Ikuo Takahashi, Yokohama;

[73] Assignee:

[22] Filed:

Yasuhiro Hasegawa, Nagoya, both of Japan Tokyo Precision Instruments Co.,

Ltd., Kanagawa-ken, Japan Nov. 7, 1972 211 Appl. No.: 304,536

[52] US. Cl. l37/625.62 [51] Int. Cl. Fl6k 11/00 [58] Field of Search..... l37/625.62, 625.61, 625.63,

References Cited 7 UNITED STATES PATENTS Chaves, Jr. et 61...... 137/85 Healy..; 137/85 Blanton. l37/625.62 X

Baltus....-. l37/625.62-

OTHER PUBLICATIONS Raymond Atchley, Inc.: Model 415 Servomotor: Brochure; page 2 of Publication Pertinent.

I Primary Examinerl-lenry T. Klinksiek Assistant Examiner-Robert J. .Miller Attorney, Agent, or Firm-Fidelman, Wolffe, Leitner & l-Iiney [5 7] ABSTRACT The present invention relates to an improved electrically-operated hydraulic servo valve in which a force feedback system is employed in positioning a spool and more particularly to improvements in the connection between the spool and a feedback spring, in which one end of the feedback spring is integrally connected with the spool and at the same time the feedback spring is made-to have a flexibility in a direction perpendicular to that of movement of the spool as well in order to accommodate the difference in locus between a circular motion of the feedback spring and a linear motion of the spool.

5 Claims, 22 Drawing Figures mamim mm 3.814.131 sumzurq Fig. 3

I06 .LI 7 z 127 I AA PRIOR ART. RI R ART Fig.7 3

B PRIOR ART PRIQR'ART FATENTEDJUH 41974 SHEET 30F 4 Fig.9

I Fig.10

- PRIOR ART M if? l PRIOR ART PATENTEUJun 41974 I sum u or 4 Fig.22

Fig. 21

BACKGROUND OF THE INVENTION Various systems of positioning an axially movable spool of an electrically-operated hydraulic servo valve have been proposed including ones with force feedback, position feedback, spring balance, pressure balance and the like. Among these, the force feedback type servo valve usually comprises a feedback spring for converting displacement of the spool into torque so as to provide a feedback to a torque motor. The servo valves of this type have certain advantages over the existing devices: (I) the linearity of the input currentoutput flow characteristics is excellent; and (2) since, in the steady state, a flapper is held in the middle position between a pair of opposed nozzles, there is little likelihood that operation of the apparatus is affected by v able, in order that a displacement of the spool may be converted into force and then into torque, has such a construction that a ball is connected withone end of the feedback spring and an opening or groove is provided in the central land of the spool to receive the ball therein. However, with this construction, a problem will arise that friction exists in the contact surfaces of the ball and the opening or groove, and the ball and the opening or groove become worn to produce a clearance therebetween, which makes the characteristics of the servo valve inferior.

By carefully working the sliding surfaces of the ball and the ball-receiving opening or groove, frictional forces may be reducedconsiderably but not satisfactorily. The input current-output flow characteristics are represented by a hysteresis loop, and in case the servo valve is used inspeed control, a limit cycle appears within the hysteresis loop, and therefore the control system often becomes unstable. I On the other hand, if a clearance is present between the sliding surfaces of the ball and the opening, a discontinuous point appears in the output flow plots. The relationship between the discontinuous flow Aq and the clearance 5 is represented by the following formula:-

where, q, and X, represent output flow and displacement of the spool, respectively, when a rated current is applied to the servo valve. Therefore, assuming that X 0.01 in q, =l5 g.p.m.

from the, above formula Aq 1.5 g.p.m. is obtained.

assembled without causing any error), the operating point will depict a limit cycle in the vicinity of the origin, thus making the system unstable.

As have been stated above, the friction which occurs between the ball connected at one end of the feedback spring and the opening or groove provided in the spool as well as the clearance produced therebetween are those disadvantageous factors inherent in the construction of the force feedback servo valve of the existing type.

SUMMARY OF THE INVENTION An object of the present invention is to provide a force feedback typeservo valve in which there is no friction between one end of a feedback spring and a spool and further no clearance is produced therebetween.

A further object of the present invention is to provide a servo valve having a design symmetry for minimizing thermal null shift thereby providing the valve with a wide temperature capability.

A'further object of the present invention is to provide a servo valve which is compact, rugged and durable against impact.

A further object of the present invention'is to provide a servo valve which is stable enough to make a zero adjustment unnecessary once it has been made.

Other objects of the present invention will be apparent from the following description of the invention taken in conjunction with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS I FIG. ltaken along lines CC;

This value can not be neglected with a high performance control system. When the servo valve having such characteristics operates in a speed control system and if the control speed U c is represented by U c qc/A (where, qc is the amount of flow at the discontinuous point and A is a piston area), the control system oscillates in a limit cycle in the vicinity of the discontinuous point. Similarly, when discontinuity occurs at a neutral position of the servo valve which is used in position control (this being the case when a torque motor, a flapper, a pair of nozzles and a guide valve are ideally FIG; 3 is a view for use in explaining the principle of theservo valve according to the present invention;

FIG. 4 is a sectional view showing a feedback spring employed in the device of FIG. 1;

FIGS. 5 through 8 show feedback springs of a force feedback servo valve heretofore available;

FIG. 9 shows a modified feedback spring of the force feedback servo valve of the existing type shown in FIGS. 5 to 8, in which the spool is displaced upon application of an input signal to the servo valve;

FIG. 10 is a characteristic curve showing the relationship between the input current and the output flow of the servo valve of the existing type;

FIGS. 11 and 12 are views showing the manner in which the feedback spring is moved longitudinally; and

FIGS. 13 to 22 show other modifications of the feedback spring and various methods of connecting the spring with the spool.

In FIGS. 1 and 2, reference numeral 1 designates a valve body having a cylindrical chamber 2 formed therein for slidably receiving a spool 3. The spool 3 is provided at both ends thereof with lands 4 and 5 and in the center thereof with a land 6. At the bottom of valve body 1 there are provided four ports l0, l1 and 43, 44 as seen in FIGS. 1 and 2. The ports 10 and 11 are communicated with an actuator, while the ports 43 and 44 are a pressurized oil port and a return port, respectively. Sleeve ports 13 and 14 communicate the re- 3 tum port 44 with the chamber 2 through achamber l5, and ports 16 and 17 communicate the pressurized oil port 43 with the chamber 2 through chambers 18 and 19, respectively.

Extending from the end wall of the chamber 2 adjacent the land 4of the spool 3 is a passage 20 which communicates with a nozzle 22. Similarly, a passage 21 extends from the opposite end wall adjacent the land and communicates with a nozzle 23 provided in opposed relationship with the nozzle 22. A flapper 24 of rigid material is provided which extends vertically at the middle position between the opposed nozzles 22 and 23. The flapper 24 is connected at its upper end with an armature 36 which is also made of rigid material. Enclosing the flapper 24 is a flexure tube 28 which is provided for mounting the armature 36 on the valve body 1. e

A feedback spring 25 having a bentportion extends downwardly of the flapper 24, and a tapered pin-like member 27 is secured at the outermost end of the spring and is received in a complementary tapered opening 26 provided in the land 6 of thespool 3.

The armature 36 is surrounded at its circumference by coils 31 and 32, and its outermost ends 29 and 30 are received in their corresponding clearance between poles of yokes 34 and 35 which are magnetically coupled with a permanent magnet 39.

A torque motor is accommodated in a space 38 defined within a housing 37 and is entirely insulated from the working fluid flowing in the valve body .1. I

Although the operational principle of the servo valve shown is known in the art, the servo valve of FIGS. 1 and 2 will now be briefly described with reference to FIGS. 3 and 4. Y 7

In abalanced condition as shown in FIG. 3, let'it be assumed-that an input current is appliedto the coils 31 and 32 so that a force is exerted on the ends 29 and 30 of the armature 36, tending to move the ends 29 and 30 downwards and upwards, respectivelyQThen, the flapper 24 is inclined against the action of the flexure tube 28 and moves towards the nozzle 23 from the central position as shown in FIG. 3. This will lower the pressure in the passage 20, that is, the pressure acting on the left side of the land 4, and simultaneously increase thepre'ssure in thepassage 21, that is, the pressure on the right side of the land 5, thereby causing the spool 3 to move leftwards. As a result, the port leading to the left side ofa cylinder (not shown) is brought into communication with the pressure port 43 through the port 16 and the chamber 8, while the port 11 leading to the right side of the cylinder is brought into communication with the return port 44 through the port 14 and the chamber 9, so that the cylinder is moved rightwards. Displacement of the spool 3 in this condition is determined by the magnitude of an input current, the rigidity of the flexure tube 28, the difference between the fluid pressures present at the nozzles 22 and 23, the magnetic force of the permanent magnet 39, and the flexibility of the feedback spring 25. It will be appreciated that if a balance is maintained between a torque applied to the armature 36 due to the input current and a force produced. by the flexibility of the feedback spring 25, and if all other forces cancel out themselves in the steady condition, then the spool displacement is conveniently made proportional to the input current. When an input current flows in the opposite direction, the spool 3 of the servo valve will move rightwards and, the port 11 is communicated with the pressure port 43 through the chamber 9 and the port 17, while the port 10 is communicated with the return port 44 through the chamber 8 and the port 13.

' The operational principle of a conventional feedback type servo valve has been described above. The present invention is primarily characterized by the provision of a feedback spring of unique shape and a methodfor connecting the end of the spring with the spool. That is, as shown in FIG. 4, the feedback spring of the servo valve according to the present invention is integrally connected with the spool, and has a bent portion so that it can extend to a required extent.

FIGS. 5, 6 and 7, 8 show examples of a method for connecting the spool of the. conventional force feedback type servo valve with the feedback spring. As illustrated, in' order to permit relative movement of the end of the spring and the spool 103 in response to spool movement, a spherical member 126 is connected at the end of the spring, which member is received ,in an opening 127 or a groove 227 provided in the central portion of the spool. The spherical member 126 slides upwards and downwards relative'to the spool and rotates. Consequently, a friction force and friction torque as shown by the arrows in FIG. 9 are produced between the spherical member 126. and the groove surfaces 227.

When such a friction force is produced, a hysteresis curve.- is depicted as shown in FIG.,10 by the relationship between the input current i and the output flow q, which adversely affects the stability and accuracy of a control system using the servo valve.

The above-stated disadvantages are removed by the feedback spring of a servo valve according to the present invention, in which the end of the spring is integrally connected with the spool and the variations in the length of the spring caused by displacement of the spool is compensated for by the initial deflection of the spring in the axial direction. This will be described with reference to FIGS. 11 and 12. When the spool is moved by X ,,the'end 26 of the spring should be displaced upwards by 8 if the spring 25 has no elongation. However, if the spring isarranged to have a flexibility and is deflected by 8 in the axial direction, the end 26 of .the spring 25 having a tapered shape is always kept II'I'CI'I- gagement with the spool and will follow the movement thereof without causing a clearance. 'Such axialflexibility may be obtained by having the spring bent in a plane perpendicular to the direction of movement of the spool. That is, deflection of the horizontal portion can provide the spring with necessary elongation.

FIGS. 13 and 14 show other modifications of the feedback spring of the servo valve according to. the present invention. The bent portion of the spring, in these modifications is in the form of a ring. Further, according to the embodiment of FIG. 14, the end 226 of the spring 25 is connected with a cylindrical pin instead of being tapered, different from the embodiments already described or shown in FIG. 13. The pin is coupled in integral with the spool by means of astop screwopening in the central portion thereof which is adapted to receive the tapered end 26 of the spring 25, flexible plates 54 and 55, and cylindrical ends 56 and 57 provided on both ends of the plate, stop screws 58 and 59 being provided to fix member 52 within the chambers 60 and 61.

FIGS. 18, 19, 20, 21 and 22 illustrate other embodiments of the present invention. According to the embodiment as shown in FIG. 18, in order to accommodate the relative movement of the spool 3 and the end 26 of the spring 25, a bellows 64 is interposed between an annular member 67 for receiving the end 26 of the spring 25 and a base member 66 secured to the spool. In the embodiment as shown in FIG. 19, a spring 65 is provided in place of the bellows 64. In the embodiments as shown in FIGS. 19 and 20, a spring is divided into two parts shown at 25 and 25, which are connected through a band-like bent spring member 68, which has the same function as that of the bent portion employed in the embodiment previously described. In the embodiments shown in FIGS. 21 and 22, the feedback spring is divided into upperand lower parts 25 and 25' similarly to that of FIGS. 19 and 20, the parts 25 and 25' being connected with each other through leaf springs 69and 70.

As has been described above, according to the invention, the end of the spring and the spool are connected integrally with each other so as not to produce friction or clearance therebetween, thus eliminating instability, preventing deterioration of accuracy and providing an increased reliability.

, Further it shouldbe understood that various modifications and improvements other than those described above may be made without departing from the spirit of invention as claimed hereinafter.

What is claimed is:

1. An electro-hydraulic servo valve comprising torque motor means including a pair of opposingly disposed yokes and an armature movably disposed between the yokes, a pair of nozzles disposed in opposed relationship, a flapper disposed between the opposed nozzles and having one end connected with the armature, a flexure tube for supporting the armature, first stage hydraulic amplifier means including a feedback spring having one end connected with the flapper, the feedback spring extending downwards, a valve body having a chamber formed therein, a spool slidably mounted within the chamber, and an output stage including ports provided in the valve body, wherein the other end of the feedback spring is removably connected to the spool for movement therewith without producing any friction.

2. An electo-hydraulic servo valve comprising torque motor means including a pair of opposingly disposed yokes and an armature movably disposed between the yokes, a pair of nozzles disposed in opposed'relationship, a flapper disposed between the opposed nozzles and having one end connected with the armature, a flexure tube for supporting the armature, first stage hydraulic amplifier means including a feedback spring having one end connected with the flapper, the feedback spring extending downwards, a valve body having a chamber formed therein, a spool slidably mounted within the chamber, and an output stage including 6 ports provided in the valve body, wherein the other end of the feedback spring is tapered so as to be fitted into an opening formed in the spool, and the feedback spring has a bent portion to provide a given initial deflection so that the tapered end is not vertically displaced.

3. An electro-hydraulic servo valve comprising torque motor means including a pair of opposingly disposed yokes and an armature movably disposed be tween the yokes, a pair of nozzles disposed in opposed relationship, a flapper disposed between the opposed nozzles andhaving one end connected with the armature, a flexure tube for supporting the armature, first stagehydraulic amplifier means including a feedback spring having one end connected with the flapper. the feedback spring extending downwards, a valve body having a chamber formed therein, a spool slidably mounted within the chamber, and an output stage including ports provided in the valve body, wherein the other end of the feedback spring is tapered so as to be fitted into an annular member provided in the spool, the annular member being connected with a base secured to the spoolthrough bellows, so that the other end of the feedback spring is connected with the spool for movement therewith without producing any friction or clearance.

4. An electro-hydraulic servo valve comprising I torque motor means including a pair of opposingly disposed yokes and anarmature movably disposed between the yokes, a pair of nozzles disposed in opposed relationship, a'flapper disposed between the opposed nozzles and having one end connected with the armature, a flexure tube for supporting the armature, first stage hydraulic amplifier means including a feedback spring having one end connected with the flapper, the feedback spring extending downwards, a valve body having a chamber formed therein, a spool slidably mounted within the chamber, and an output stage including ports provided in the valve body, wherein the other end of thefeedback spring is-connected with the spool for movement therewith, the spring being divided into two parts so that the spring has necessary flexibility, the feedback spring being coupled through spring means for permitting expansion of the feedback spring.

5. An electro-hydraulic servo valve comprising torque motor means including a pair of opposingly disposed yokes and an armature movably disposed between the yokes, a pair of nozzles disposed in opposed relationship, a flapper disposed between the opposed nozzles and having one end connected with the armaperpendicular to the spool as the spool moves. 

1. An electro-hydraulic servo valve comprising torque motor means including a pair of opposingly disposed yokes and an armature movably disposed between the yokes, a pair of nozzles disposed in opposed relationship, a flapper disposed between the opposed nozzles and having one end connected with the armature, a flexure tube for supporting the armature, first stage hydraulic amplifier means including a feedback spring having one end connected with the flapper, the feedback spring extending downwards, a valve body having a chamber formed therein, a spool slidably mounted within the chamber, and an output stage including ports provided in the valve body, wherein the other end of the feedback spring is removably connected to the spool for movement therewith without producing any friction.
 2. An electo-hydraulic servo valve comprising torque motor means including a pair of opposingly disposed yokes and an armature movably disposed between the yokes, a pair of nozzles disposed in opposed relationship, a flapper disposed between the opposed nozzles and having one end connected with the armature, a flexure tube for supporting the armature, first stage hydraulic amplifier means including a feedback spring having one end connected with the flapper, the feedback spring extending downwards, a valve body having a chamber formed therein, a spool slidably mounted within the chamber, and an output stage including ports provided in the valve body, wherein the other end of the feedback spring is tapered so as to be fitted into an opening formed in the spool, and the feedback spring has a bent portion to provide a given initial deflection so that the tapered end is not vertically displaced.
 3. An electro-hydraulic servo valve comprising torque motor means including a pair of opposingly disposed yokes and an armature movably disposed between the yokes, a pair of nozzles disposed in opposed relationship, a flapper disposed between the opposed nozzles and having one end connected with the armature, a flexure tube for supporting the armature, first stage hydraulic amplifier means including a feedback spring having one end connected with the flapper, the feedback spring extending downwards, a valve body having a chamber formed therein, a spool slidably mounted within the chamber, and an output stage including ports provided in the valve body, wherein the other end of the feedback spring is tapered so as to be fitted into an annular member provided in the spool, the annular member being connected with a base secured to the spool through bellows, so that the other end of the feedback spring is connected with the spool for movement therewith without producing any friction or clearance.
 4. An electro-hydraulic servo valve comprising torque motor means including a pair of opposingly disposed yokes and an armature movably disposed between the yokes, a pair of nozzles disposed in opposed relationship, a flapper disposed between the opposed nozzles and having one end connected with the armature, a flexure tube for supporting the armature, first stage hydraulic amplifier means including a feedback spring having one end connected with the flapper, the feedback spring extending downwards, a valve body having a chamber formed therein, a spool slidably mounted within the chamber, and an output stage including ports provided in the valve body, wherein the other end of the feedback spring is connected with tHe spool for movement therewith, the spring being divided into two parts so that the spring has necessary flexibility, the feedback spring being coupled through spring means for permitting expansion of the feedback spring.
 5. An electro-hydraulic servo valve comprising torque motor means including a pair of opposingly disposed yokes and an armature movably disposed between the yokes, a pair of nozzles disposed in opposed relationship, a flapper disposed between the opposed nozzles and having one end connected with the armature, a flexure tube for supporting the armature, first stage hydraulic amplifier means including a feedback spring having one end connected with the flapper, the feedback spring extending downwards, a valve body having a chamber formed therein, a spool slidably mounted within the chamber, and an output stage including ports provided in the valve body, wherein the other end of the feedback spring is secured to the spool by means of a flexible plate member provided in the spool, the plate member extending in an axial direction of the spool, the plate member being bent in a direction perpendicular to the spool as the spool moves. 